Seismic evidence for an 850 km thick low‐velocity structure in the Earth's lowermost mantle beneath Kamchatka
Seismic evidence for an 850 km thick low‐velocity structure in the Earth's lowermost mantle beneath Kamchatka
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DOI：
10.1002/2014gl061249
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发表时间：
2014-10
影响因子：
5.2
通讯作者：
Yumei He;L. Wen;T. Zheng
中科院分区：
文献类型：
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作者：
Yumei He;L. Wen;T. Zheng
我们在堪察加半岛下的地球最低地幔中探测到一个850公里厚的低速结构，该结构被一个210公里厚的高速D“”结构包围并覆盖。通过模拟在90°至100°的大距离处记录的对最低地幔采样的地震剪切波的观测到的异常加宽的波形来约束速度结构。波形模拟分析表明，低速异常在地幔最低210 km处有一个直径约550 km的茎，以及一个直径约1600 km的帽。帽盖的低速结构从顶部的0%下降到核幔边界（CMB）上方约400 km处的-1.5%，210 km处的-1.2%。我们认为，低速异常的几何和速度特征表明，它可能代表了一个局部的地幔柱在下地幔中以前未被发现。
We detect an 850 km thick low‐velocity structure in the Earth's lowermost mantle beneath Kamchatka surrounded by and overlying a 210 km thick high‐velocity D′′ structure. The velocity structure is constrained by modeling the observed anomalously broadened waveforms for seismic shear waves sampling the lowermost mantle recorded at large distances from 90° to 100°. Waveform modeling analyses reveal that the low‐velocity anomaly has a stem with a diameter of about 550 km in the lowermost 210 km of the mantle and a cap with a diameter of about 1600 km. The low‐velocity structure of the cap decreases from 0% at the top to −1.5% at about 400 km above the core‐mantle boundary (CMB) and to −1.2% at 210 km above the CMB. We suggest that the geometrical and velocity features of the low‐velocity anomaly indicate that it may represent a localized mantle plume undetected before in the lower mantle.